强流直线感应加速腔微波特性

Microwave characteristics of high current linear induction accelerator cavity

介绍了确定不同加速间隙形状和设计结构的强流直线感应加速腔微波特性的方法,即确定频域中加速腔横向阻抗值的方法,包括数值模拟和实验测试。横向阻抗测试实验中采用了两种测试方法:一种为同轴线束流模拟法,另一种为对加速腔形状因子的测试。实验中测试了3种不同的腔型,并和数值模拟结果进行了比较。两种横向阻抗的测试方法所得结果都与计算结果基本符合,从测试过程的繁简程度和多次实验结果的重复性来看,对于强流直线感应加速腔来说,形状因子值测试方法优于双芯同轴线束流模拟法。实验测试和数值模拟结果显示,确定直线感应加速腔横向阻抗值,测试实验和数值模拟是相辅相成的,缺一不可。

Methods to determine the transverse impedance＇ of a linear induction accelerator（LIA） cavity both in calculation and experiment were introduced. To minimize transverse impedance is very important in designing induction cavities for an LIA, since for a new designed cavity to investigate its RF fields related to the shape of the accelerating gap is in very high priority. Three different cavities were chosen as models, accelerating cavities of a 10 MeV LIA and “Dragon-I”, and a non-accelerating cavity of ＂Dragon-I＂ designed for vacuum pump and beam diagnosis. Both coaxial line method and η factor method were employed in experimental tests. The main parts of the device used in both methods were identical, which was a coaxial line with two off center inner conductors formed by one under test cavity and two beam tubes with the same inner diameter of the cavity. The difference was that the coaxial line method measures the S parameters of the device and the η factor one measures the spatial RF signal both in accelerating gap and near the wall of the beam tube by a B-dot. A swept RF signals were fed into the device at the same time. Both the experimental results and the simulative ones are presented. Both the results of the two experimental methods are coincident with the calculated one. Comparing the two methods, the η factor method is more attractive because of easy manipulation and repeatablility although the raw data need to be processed and corrected.